This invention relates to selective detection of vapors and more particularly to the high speed, highly sensitive and selective detection of specific gas-chromatographically-separable compounds, especially certain nitrogen-containing compounds such as methamphetamine, cocaine, and heroin.
Instruments are known which utilize gas chromatographs to separate constituents of a gas sample and then detect specific compounds among the separated constituents. For example, U.S. Pat. Nos. 4,778,764 and 4,843,016 to Fine, whose disclosures are incorporated herein by reference to those patents, describe an apparatus and method for detecting nitrogen-containing compounds in a sample by chromatographically separating constituents, heating the separated constituents in the presence of oxygen to convert bound nitrogen to nitric oxide (NO) gas, and then detecting the nitric oxide gas to determine the presence of the compounds. Apparatus employing similar basic concepts, which operates to separate then pyrolyze and detect nitrogen-containing compounds known as N-nitrosamines, is described in U.S. Pat. No. 4,301,114 (Rounbehler et al.) whose disclosure is also incorporated herein by reference to that patent.
In certain detection applications neither excluded from nor described in the above-referenced Fine patents, it is important that sample analyses be performed quickly and with high selectivity and sensitivity. For example, air samples containing vapors of explosives or drugs acquired from surfaces such as the clothing or luggage of person, or from containers, must be processed quickly and accurately by a detector for the instrument to be useful in screening personnel or articles passing in quantity through a checkpoint. High sensitivity is needed for detection of minute quantities of specific vapors which may be present in gas (e.g., air) samples acquired in relatively short time intervals. High selectivity is essential for accurate detection, particularly for avoiding false alarms which may be triggered if vapors from compounds not of interest Produce signals which are not clearly separable from those produced by compounds of interest. Selectivity can be difficult to achieve for "dirty" samples containing many compounds, particularly if time and/or equipment for clean-up of individual (or successive) samples are not available.
Accordingly, it is an object of the invention to provide an improved method and apparatus for detecting vapors of specific compounds separable by gas chromatography.
It is an object of the invention to provide a high speed, highly selective system and method for detecting vapors of specific gas-chromatographically (GC)-separable nitrogen-containing compounds.
It is a particular object of the invention to provide a high speed, highly selective method and apparatus for detecting vapors of drugs such as methamphetamine, cocaine, and heroin.
It is a particular object of the invention to provide a high speed, highly selective method and apparatus for detecting vapors of GC-separable compounds in which the vapors of at least one specific compound of interest have substantially higher volatility than the vapors of at least one other specific compound of interest.
It is a particular object of the invention to provide a method and apparatus which achieve the foregoing objectives without diverting a portion of each gas sample from passage through the second of two series-connected gas chromatographs.